<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>检测 cookie 值的函数</title>
    <script>
        function setCookie(cname, cvalue, exdays) {
            var d = new Date();
            d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
            var expires = "expires=" + d.toGMTString();
            document.cookie = cname + "=" + cvalue + "; " + expires;
        }
        function getCookie(cname) {
            var name = cname + "=";
            var ca = document.cookie.split(';');
            for (var i = 0; i < ca.length; i++) {
                var c = ca[i].trim();
                if (c.indexOf(name) == 0) { return c.substring(name.length, c.length); }
            }
            return "";
        }
        function checkCookie() {
            var user = getCookie("username");
            if (user != "") {
                alert("欢迎 " + user + " 再次访问");
            }
            else {
                user = prompt("请输入你的名字:", "");
                if (user != "" && user != null) {
                    setCookie("username", user, 30);
                }
            }
        }
    </script>
</head>

<body onload="checkCookie()">

</body>

</html>